1. Field of the Invention
The present invention relates to a multi-layered information recording medium comprising at least two recording layers, a reproduction apparatus, a recording apparatus for use with the multi-layered information recording medium, a reproduction method for reproducing information from the multi-layered information recording medium, and a recording method for recording information in the multi-layered information recording medium.
2. Description of the Related Art
A typical information recording medium which has a sector structure is an optical disc. In recent years, AV data, such as audio data, video data, and the like, has been digitalized, and accordingly, an optical disc having a higher recording density and a larger capacity has been demanded. Providing a plurality of recording layers is useful in increasing the capacity of a disc. For example, the capacity of a read-only DVD has been increased about two times by providing two recording layers to the DVD.
FIG. 1 shows a structure of a typical optical disc medium 1 including a track 2 and sectors 3. On the optical disc medium 1, the track 2 is turned multiple times in a spiral arrangement. The track 2 is divided into a large number of small sectors 3. Regions formed on the disc medium 1 are roughly classified into a lead-in area 4, a user data area 8, and a lead-out area 6. Recording or reproduction of user data is performed on the user data area 8. The lead-in area 4 and the lead-out area 6 are provided as margins such that an optical head (not shown) can appropriately follow a track even if overrunning of the optical head occurs when the optical head approaches an end portion of the user data area 8. The lead-in area 4 includes a disc information area which stores parameters necessary for accessing the disc medium 1. Physical sector numbers (hereinafter, abbreviated as “PSN(s)”) are assigned to the sectors 3 in order to identify the respective sectors 3. Further, consecutive logical sector numbers (hereinafter, abbreviated as “LSN(s)”) which start with 0 are assigned to the sectors 3 included in the user data area 8 such that a high level apparatus (not shown) such as a host computer identifies the respective sectors 3.
FIG. 2 illustrates a principle of reproduction of data from a read-only optical disc 30 having two recording layers. Here, production of the read-only optical disc 30 of FIG. 2 is briefly described. Grooves are formed on transparent substrates 31 and 32 so as to form spiral tracks. Over the grooved surfaces of the substrates 31 and 32, recording layers 33 and 34 are attached so as to cover the grooved surfaces, respectively. The substrates 31 and 32 are attached together so as to sandwich a transparent light-curable resin 35 between the recording layers 33 and 34, thereby obtaining a single read-only optical disc 30. In this specification, for convenience of description, in FIG. 2, a recording layer 34 closer to the incoming laser light 38 is referred to as a first recording layer 34; whereas the other recording layer 33 is referred to as a second recording layer 33. The thickness and composition of the first recording layer 34 are adjusted such that the first recording layer 34 reflects a half of the incoming laser light 38 and transmits the other half of the incoming laser light 38. The thickness and composition of the second recording layer 33 are adjusted such that the second recording layer 33 reflects all of the incoming laser light 38. An objective lens 37 for converging the laser light 38 is moved toward or away from the read-only optical disc 30 such that the convergence point (beam spot) 36 of the laser light 38 is placed on the first recording layer 34 or the second recording layer 33.
FIGS. 3A, 3B, 3C and 3D show tracks of two recording layers 41 and 42 of a read-only DVD, which are called parallel paths, and the reproduction direction and sector numbers. FIG. 3A shows a spiral groove pattern of the second recording layer 42. FIG. 3B shows a spiral groove pattern of the first recording layer 41. FIG. 3C shows the reproduction direction in user data areas 8 provided on the recording layers 41 and 42. FIG. 3D shows sector numbers assigned to the recording layers 41 and 42.
Now, consider the read-only DVD disc is rotated clockwise when it is viewed from the back face side of the disc in the direction along which laser light comes onto the disc, i.e., when it is viewed from the back side of the sheets of FIGS. 3A and 3B. In this case, the laser light moves along the track 2 from the inner periphery to the outer periphery of the recording layers 41 and 42. In the case where user data is sequentially reproduced along the reproduction direction shown in FIG. 3C, reproduction is first performed from the innermost periphery to the outermost periphery of the user data area 8 of the first recording layer 41. Then, reproduction is performed from the innermost periphery to the outermost periphery of the user data area 8 of the second recording layer 42. The user data areas 8 of the first and second recording layers 41 and 42 are sandwiched by the lead-in area 4 and the lead-out area 6 such that an optical head can appropriately follow the track 2 even if overrunning of the optical head occurs. As shown in FIG. 3D, the PSNs and LSNs of each of the recording layers 41 and 42 are incrementally assigned along the reproduction direction. The PSNs do not necessarily need to start with 0 in view of convenience of disc formation. Further, the PSNs do not necessarily need to be continuously assigned between the first and second recording layers 41 and 42 (for example, a value corresponding to the layer number may be provided at the first location of each sector number). As LSNs, consecutive numbers which start with 0 are assigned to all of the user data areas 8 included in the optical disc. That is, in the user data area 8 of the first recording layer 41, the LSN at the innermost periphery is 0, and increases by ones toward the outermost perimeter. The LSN at the innermost periphery of the user data area 8 of the second recording layer 42 is a number obtained by adding 1 to the maximum LSN of the first recording layer 41. The LSN of the second recording layer 42 also increments by ones toward the outermost perimeter.
FIGS. 4A, 4B, 4C and 4D show tracks of two recording layers 43 and 44 of a read-only DVD, which is called an opposite path arrangement, and the reproduction direction and sector numbers. FIG. 4A shows a spiral groove pattern of the second recording layer 44. FIG. 4B shows a spiral groove pattern of the first recording layer 43. FIG. 4C shows the reproduction direction in user data areas 8 provided on the recording layers 43 and 44. FIG. 4D shows sector numbers assigned to the recording layers 43 and 44.
Now, consider the read-only DVD disc is rotated clockwise when it is viewed from the back face side of the disc in the direction along which laser light comes onto the disc, i.e., when it is viewed from the back side of the sheets of FIGS. 4A and 4B. In this case, the laser light moves along the track 2 from the inner periphery to the outer periphery in the first recording layer 43, but from the outer periphery to the inner periphery in the second recording layer 44. In the case where user data is sequentially reproduced along the reproduction direction shown in FIG. 4C, reproduction is first performed from the innermost periphery to the outermost periphery of the user data area 8 of the first recording layer 43, and then, reproduction is performed from the outermost periphery to the innermost periphery of the user data area 8 of the second recording layer 44. The user data area 8 of the first recording layer 43 is sandwiched by the lead-in area 4 and a middle area 7 such that an optical head can appropriately follow the track 2 even if overrunning of the optical head occurs. The user data area 8 of the second recording layer 44 is sandwiched by the middle area 7 and the lead-out area 6. The function of the middle area 7 is the same as that of the lead-out area 6. As shown in FIG. 4D, the PSNs and LSNs of each of the recording layers 43 and 44 are incrementally assigned along the reproduction direction as in the above-described parallel paths, except that the relationship between the sector numbers and the radial direction is changed because the spiral direction of the track 2 of the second recording layer 44 is inverse to the spiral direction of the track 2 of the first recording layer 43. In the user data area 8 of the first recording layer 43, the LSN is 0 at the innermost periphery, and increments by ones toward the outer periphery. The LSN at the outermost periphery in the user data area 8 of the second recording layer 44 is a number obtained by adding 1 to the maximum LSN in the user data area 8 of the first recording layer 43, and increments by ones toward the innermost perimeter.
Above, read-only optical discs have been described. Now, features specific to a rewritable optical disc are described. Such features result from the fact that requirements on a margin for a recording operation are more severe than that for a reproduction operation.
FIG. 5A shows an area layout of a typical rewritable disc 45. The rewritable disc 45 includes only one recording layer. A lead-in area 4 of the rewritable disc 45 includes a disc information area 10 and an OPC (Optimum Power Calibration) area 11, and a defect management area 12. The lead-out area 6 includes another defect management area 12. A user data area 8 and a spare area 13 are provided between a lead-in area 4 and a lead-out area 6.
A disc information area 10 stores disc information regarding a parameter(s) or a format necessary for recording/reproduction of data of the optical disc. The disc information area 10 is also included in a read-only optical disc, but the disc information area 10 of the read-only optical disc includes nothing important other than a format identifier used for identifying the optical disc. On the other hand, in a rewritable optical disc, specific recommended values for the characteristics of the laser light used for recording, such as laser power, pulse width, and the like, are stored for each generated mark width. The disc information area 10 is a read-only area in which information is typically written at the time of production of the disc. In the rewritable disc 45, pits are formed in the disc surface as in a DVD-ROM or a CD-ROM. (There is a recording principle different from such a “pit” recording principle. For example, in a CD-RW, information is embedded in a meandering pattern (called “wobble”) of a groove.)
The OPC area 11 is provided for optimally adjusting the recording power of laser light. A disc manufacturer stores recommended laser parameters for a recording operation in the disc information area 10. However, a laser element used by the disc manufacturer for obtaining the recommended values is different from a laser element incorporated in an optical disc drive apparatus, in respect to laser characteristics, such as the wavelength, the rising time of the laser power, and the like. Further, even a laser element of the same optical disc drive, the laser characteristics thereof vary because of a variation of the ambient temperature or deterioration which occurs over time. Thus, in an actual case, test recording is performed on the OPC area 11 while increasingly and decreasingly changing the laser parameters stored in the disc information area 10 so as to obtain an optimum recording power.
A defect management area 12 and a spare areas 13 are provided for defect management, i.e., provided for replacing a sector of the user data area 8 in which recording/reproduction cannot be appropriately performed (referred to as a “defective sector”) with another well-conditioned (i.e., sufficiently usable) sector. In a rewritable single-layer optical disc, such as a 650 MB phase-change optical disc (called a PD) defined in the ECMA-240 format, or the like, defect management is generally performed.
The spare area 13 includes a sector for replacing a defective sector (referred to as a spare sector). A sector which is already employed in place of a defective sector is referred to as a replacement sector. In a DVD-RAM, spare areas 13 are placed at two positions, one at the inner periphery and the other at the outer periphery of the user data area 8. In the above-described PD, spare areas 13 are provided at 10 positions, and their arrangement varies depending on the medium. In the example of FIG. 5, for the sake of simplicity, a spare area 13 is provided at only one portion at the outer periphery of the user data area 8.
The defect management area 12 includes: a disc definition structure (DDS) storing area 20 storing a format designed for defect management, which includes the size of the spare area 13 and the position where the spare area 13 is placed; a defect management sector (DMS) storing area 21 storing data for managing the defect of the defect management area 12 itself; a defect list (DL) storing area 22 storing a list of defects containing the positions of defective sectors and the positions of replacement sectors; and a spare defective list (spare DL) storing area 23 which is used to replace the defect list (DL) storing area 22 when it is not usable. In view of robustness, many discs are designed based on a specification such that each of the inner perimeter portion and outer perimeter portion of a disc has one defect management area 12, and each defect management area 12 duplicately stores the same contents, i.e., the defect management areas 12 of the disc have the four copies of the same contents in total.
FIG. 5B shows data stored in a DMS 21. The data stored in the DMS 21 are the number of DL sectors 30 which indicates the number of sectors storing a defect list, and a list of DL sector addresses 31 each of which indicates the address of a sector. For the sake of simplicity, DL storing areas 22 each are herein assumed to include only one sector. If it is determined that a DL storing area 22 is defective when updating a defect list because of detection of a new defective sector, the following spare DL storing area 23 is used to record the defect list. In this case, the DL sector address list 31 is updated so as to indicate the sector address of the spare DL storing 23.
FIG. 5C shows data stored in a DL storing area 22. The data stored in the DL storing area 22 area DL identifier 32 which is a unique identifier for identifying a defect list, and the number of defective sectors 33 registered on the defect list. The DL storing area 22 further includes a plurality of defect entry areas 34 each including the address of a defective sector and the address of a replacement sector. It is now assumed that there are n defects registered (n is an integer greater than or equal to 3). In this case, the number of defective sectors 33 indicates n.
A first defect entry area 34 stores a replacement status 40, a defective sector address 41, and a replacement sector address 42. In other words, a single defect entry area stores information relating to a process for replacing a single defective sector. The replacement status 40 is a flag indicating whether or not replacement is applied to a defective sector. When replacement is performed, a value 0 is set in the replacement status 40. When replacement is not applied, a value 1 is set in the replacement status 40. When the value 1 is set in the replacement status 40, an optical disc drive apparatus accesses a defective sector. In this case, even if an error occurs in a read out process, the error is ignored and the read out process is continued while data contains the error. Such a process may be applied for recording and reproduction of video and audio data requiring continuous recording or reproduction. This is because interruptions in reproduction of video or audio due to replacement of a defective area with a distant spare area appears more significant than disturbances in video or audio due to the erroneous data itself. The defective sector address 41 contains the address of a sector which is determined to be defective. The replacement sector address 42 contains the address of a sector in a spare area 13, which sector replaces a defective sector indicated by the defective sector address 41. The n defect entry areas are arranged in ascending order of the address of a defective sector.
As described above, defect management is essential for rewritable optical discs to obtain substantially the same data reliability as that of read-only optical discs.
Although there are read-only optical discs having a plurality of recording layers, all existing rewritable optical discs have only a single recording layer. The above-described defect management for a rewritable optical disc is directed to management of only one recording layer.
If defect management as described above was simply applied to an optical disc having a plurality of recording layers, a defect management area would be provided for each recording layer. A defect management is separately performed for each recording layer. A typical recording/reproduction apparatus for rewritable optical discs transfers a defect list into a memory within the apparatus when the apparatus is actuated (initial process). This is because defect management information can be accessed at high speed, which is constantly referenced in recording and reproduction of user data. Therefore, when a recording/reproduction apparatus handles an optical disc having a plurality of recording layers, the apparatus needs to read all defect management areas in all recording layers when loading a disk into the apparatus. This poses a problem such that it takes a long time before starting actual recording or reproduction of a disc. Moreover, defect management is separately performed for each recording layer, and therefore, if a finite defect list storing area is exhausted in a certain recording layer, any defect list storing areas of other recording layers are not available for that exhausted recording layer. This poses a problem such that defect list storing areas cannot be efficiently used.
As used herein, the term “initial process” for an optical disc refers to a process in which defect management information or the like is read out before recording or reproduction user data or the like on the disc when a recording/reproduction apparatus is actuated.